MEMS-based M×N optical switches are currently being developed for use in optical switching systems, such as the optical switching systems used to switch optical signals from one optical fibre to another in an optical network. In such an optical switch, an optical signal received via an input fibre illuminates a first steerable mirror. The input fibre is one of M input fibres. The first steerable mirror is associated with the input fibre and steers the optical signal towards a second steerable mirror. The second steerable mirror is associated with an output fibre. The output fibre is one of N output fibres. The second steerable mirror reflects the optical signal received from the first steerable mirror into the output fibre.
In such an optical switch, the angle of each of the steerable mirrors must be accurately set to a precision in the order of 1 part in 213 to couple the optical signal from the input fibre to the output fibre with a high coupling efficiency. When the input and output fibres are arrayed in two-dimensional arrays, the angle of the steerable mirrors must be set with the required precision about each of two orthogonal axes. Complex, closed-loop positioning mechanisms are required to achieve this accuracy.